Electronic structure of wurtzite and zinc-blende AlN

The electronic structure of AlN in wurtzite and zinc-blende phases is studied experimentally and theoretically. By using x-ray emission spectroscopy, the Al 3p, Al 3s and N 2p spectral densities are obtained. The corresponding local and partial theoretical densities of states (DOS), as well as the total DOS and the band structure, are calculated by using the full potential linearized augmented plane wave method, within the framework of the density functional theory. There is a relatively good agreement between the experimental spectra and the theoretical DOS, showing a large hybridization of the valence states all along the valence band. The discrepancies between the experimental and theoretical DOS, appearing towards the high binding energies, are ascribed to an underestimation of the valence band width in the calculations. Differences between the wurtzite and zinc-blende phases are small and reflect the slight variations between the atomic arrangements of both phases

Rare earth rhodium borides RRh3B (R = Y, Zr, and Nb): mechanical, thermal and optical properties

We report here ab initio density functional theory (DFT) calculations of structural, elastic, Peierls stress, thermodynamic and optical properties of RRh3B (R =  Y, Zr and Nb) using the plane wave pseudopotential method. The materials possess better ductile behavior in comparison with a selection of layered MAX phases but the anisotropy is strong, particularly in NbRh3B. The Peierls stress, approximately 3-4 times larger than in MAX phases, show that dislocation movement may follow but with much reduced occurrences compared to MAX phases. The temperature and pressure dependence of bulk modulus, specific heats, thermal expansion coefficient, and Debye temperature are calculated for the first time for two of the three compounds using the quasi-harmonic Debye model with phononic effects for elevated temperature and pressure. The obtained results are discussed in comparison to the behavior of other related compounds. Further the features of optical functions obtained for the first time are discussed. The study reveals that the reflectivity is high in the IR-UV regions up to  ~17.5 eV (YRh3B, ZrRh3B) and 20 eV (NbRh3B), thus showing promise as good coating materials